Robotic assembly machines often utilize video cameras to observe a component, part or work piece being handled, machined or assembled. For instance, in the assembly of electronic components, chips or wafers are often assembled into printed circuit boards by robots utilizing video cameras to position the components and/or to inspect the assembled device for defects throughout the process. In the microelectronics industry, solder pads on surface-mount devices are often observed by machine vision systems for assembly and manufacturing purposes. The accuracy and reliability of a machine vision system is critical for proper alignment of the numerous components which are to be mounted on a printed circuit board. For optimum alignment, solder pads must be clearly observed in high contrast with their background.
Proper illumination of many different shiny and uneven surfaces, such as solder connections, foil packaging, ball bearings, etc., is critical if high quality robotics assembly is to be achieved. However, such shiny and uneven surfaces are difficult to illuminate for accurate video imaging, and this creates a need for improved illumination of such objects being observed by machine vision cameras.
When using previously available illumination systems to illuminate work pieces having uneven, highly reflective surfaces, the uneven reflection of light from these surfaces frequently produces erroneous images and signals when viewed through the camera, thereby possibly resulting in an erroneous signal or incorrect/inaccurate measurement. Errors of one or two thousandths of an inch in a fiducial location measurement for a single component are sufficient to ruin a large and expensive circuit board. Furthermore, previously available illumination systems for robotics handling of items have not produced a light which is uniform over the entire object being observed. As a result, the reflected image suffers from erroneous shadows, glints and glare thereby rendering it difficult to determine the precise location or quality of the object.
To date, many illumination devices have been developed to provide substantially uniform illumination of an object to be viewed. For example, U.S. Patent Publication No. 2008/0106794 to Messina, which is incorporated herein by reference in its entirety, discloses illuminating a component via a beamsplitter comprising at least three distinct light-reflection zones. The beamsplitter can illuminate a component with light energy reflected from each of a plurality of distinct light reflection zones.
Similarly, U.S. Pat. No. 5,761,540 to White, which is also incorporated herein in its entirety, discloses an illumination device for illuminating an object to be observed by a machine vision camera or the like with a continuous diffuse wide-angle light along the observation axis of the machine vision camera. A diffuser is mounted parallel to the observation axis, but is separated from a beamsplitter by a microlouver filter so that the microlouver filter prevents diffused light from the diffuser from directly illuminating any point of interest on the surface of the object to be observed.